The invention concerns a superconducting magnetic field coil comprising at least one coil section which is wound in layers.
Magnetic field coils of this type are disclosed e.g. by the NMR magnets of the UltraShield product line of the company Bruker BioSpin GmbH, Rheinstetten, DE.
Superconducting magnetic field coils are used to generate magnetic fields of high strength (approximately 20 Tesla or more). Magnetic fields of such high strength are used, in particular, in high-resolution nuclear magnetic resonance (NMR) spectroscopy. Superconducting magnetic field coils are cooled during operation, e.g. using liquid helium in a cryostat.
The magnetic field coils typically have a solenoidal shape and are wound from superconducting wire in layers which are disposed on top of each other and connected in series. The superconducting wire is generally tightly wound within one layer, i.e. neighboring windings of the superconducting wire contact each other. This prevents the windings from being displaced by magnetic forces, in particular, when the magnetic field coil is charged.
Individual parts of the superconducting wire can only be combined outside of the coil using superconducting connecting elements, so-called joints. One piece of wire is therefore conventionally always used to wind an integer number of layers. For producing the coil, only that portion of a wire piece is used which corresponds to the length of an integer multiple of the “layer length” (this is the wire length within one layer). Any residue of the wire piece is discarded (“waste”).
Since the production of wires from Nb3Sn or NbTi superconductors is usually based on bolts of a weight of typically approximately 30 kg to 300 kg, the available wire piece length is determined to a large degree by the conductor cross-section of the wire. In high-temperature superconductors, such as YBaCuO or BiSrCaCuO, the maximum available wire piece length is currently between approximately 100 m and approximately 2000 m.
For magnet coils having very short layer lengths compared to the available wire piece lengths (e.g. due to a short layer length with small coil diameter and/or a thin conductor cross-section e.g. with a conductor weight<10 kg/layer), the waste can be neglected compared to the overall production costs.
For magnetic field coils with layer lengths of the same magnitude as the available lengths of wire pieces (e.g. due to a large coil diameter and/or a large conductor cross-section and therefore high conductor weight/layer, approximately>10 kg/layer), the superconducting wire waste considerably increases the production costs of the magnetic field coil. If e.g. a wire piece of a length corresponding to 1.9 layers is available, the remaining wire of a length that corresponds to 0.9 layers is discarded, e.g. the waste can almost double the material costs for the superconducting wire.
It is therefore the underlying purpose of the present invention to provide a superconducting magnetic field coil which can be produced at much less cost than conventional magnetic field coils, in particular, when the magnetic field coil has a comparatively large layer length.